High-temperature getters for electronic tubes



May 14, 1957 D. o. HOLLAND HIGH-TEMPERATURE GETTERS FOR ELECTRONIC TUBES Filed Sept. 18. 1953 d n a w m D United rates Fatent HIGH-TEMPERATURE GETTERS FGR ELECTRONIC TUBES Donald 0. Holland, Newton Center, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application September 18, 1953, Serial No. 381,093

4 Claims. (Cl. 313-474) This invention relates to electronic tubes generally, whether formed in tubular, spherical or other shape, and in particular to thermionic tubes having a hot element, usually an incandescent filament, such as a cathode or a cathode heater having a coating, usually of oxide, to improve electron emission or to serve as insulation or both.

In the manufacture of such tubes it is customary to remove residual gas by means of so-called getters which are active chemical substances, such as barium and magnesium, which combine with certain gases when heated. Sometimes the getter substances are flashed but this invention relates particularly to getters in which the substances are merely heated to temperatures below the flashing point. The invention is particularly useful in tubes which operate at high temperatures, such as the modern miniature tubes where most substances, such as barium, degas at the high temperature. In tubes where the getter is near the hot element there is danger of injury to the aforesaid coating due to chemical reaction between the coating and the active getter material if they come into contact while hot.

Objects of the invention are to remove the residual gases and keep them removed at high temperatures, to provide a thermionic tube in which the getter can be closely associated with the hot element without danger of damage to its coating, to increase the efiiciency of the getter, and generally to improve tubes of the type referred to.

In one aspect the invention involves a hollow hot element, such as a heated cathode or cathode heater, and a getter inside the hot element. In the case of a cathode heated indirectly, preferably the cathode is hollow, the

heater is inside the cathode and the getter is inside the heater.

In another aspect the invention involves a tube comprising a cathode, a heater, and a getter on the side of the heater opposite the cathode. In the case of a hollow heater the getter should be on the inner side of the heater, and in the case of a helical heater the getter is preferably disposed along its axis. With a tubular cathode, the getter, heater and cathode are preferably arranged concentrically. The getter should include a shield of material which is inert to the hot elements and the getter material when hot, the shield having spaces to admit gas to the getter material. Preferably the shield is in the form of a wire helix around a core of getter material with spaces between turns to admit gas to the getter material.

For the purpose of illustration a typical embodiment of the invention is shown in the accompanying drawings in which:

Fig. I is a longitudinal central section of a tube built according to the present invention; and

Fig. 2 is an end view from line 2-2 of Fig. 1.

Patented May 14, 1957 The particular embodiment of the invention chosen for the purpose of illustration comprises a metallic envelope 1 which also serves as an anode, a metallic base ring 2 soldered to the envelope at 3, an insulating disk 4 sealed in the ring 3, a tubular cathode 5, a cathode heater 6 and a getter comprising a core 7 and a shield 8 of wire wound spirally around the core with spaces between turns. While the heater may be any suitable type, in the illustration it is a double spiral coil. The core 7 is preferably formed of zirconium and the shield wire 8 of tungsten. Zirconium will not only get and keep tube gases at temperatures above 850 C. but it is an increasingly eliective getter with increasing temperature up to 1200 C. Thus by locating a getter of this kind inside the hot element (the cathode heater in the illustration) exceptionally good results are obtained. However when the getter is close to the hot element it must be shielded as aforesaid to guard against accidental contact with the hot element because of its great chemical atfinity for the coating of the hot element. For example, when using a zirconium getter with an alumina coating on the heater the reaction is 3Zr+2Al2O3=3ZrO2+4AL thereby producing gas and causing cathode leakage.

The getter and heater assembly is preferably made by first winding the shield wire on the getter core and then inserting the core and shield assembly into the heater coil.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. In an electronic tube, a cathode heater element comprising a coiled filament coated with a refractory insulating material, a core of a zirconium getter located within and supported by the coils of said filament and a shield of a highly refractory metal interposed between said filament and said core, said shield having an opening therein to permit access of gas to said core.

2. In an electronic tube, a cathode heater element comprising a coiled filament coated with a refractory insulating material, a core of a zirconium getter located within and supported by the coils of said filament and a shield of tungsten interposed between said filament and said core, said shield having an opening therein to permit access of gas to said core.

3. In an electronic tube, a cathode heater element comprising a coiled filament coated with a refractory insulating material, a core of zirconium getter located within and supported by the coils of said filament and a shield of a highly refractory metal interposed between said filament and said core, said shield comprising a wire helix around said core with spaces between turns to permit access of gas to said core.

4. In an electronic tube, a cathode heater element comprising a coiled filament coated with a refractory insulating material, a core of a zirconium getter located within and supported by the coils of said filament and a shield of tungsten interposed between said filament and said core, said shield comprising a wire helix around said core with spaces between turns to permit access of gas to said core.

References Cited in the file of this patent UNITED STATES PATENTS 2,469,626 Beers May 10, 1949 

1. IN AN ELECTRONIC TUBE, A CATHODE HEATER ELEMENT COMPRISING A COILED FILAMENT COATED WITH A REFRACTORY INSULATING MATERIAL, A CORE OF A ZIRCONIUM GETTER LOCATED WITHIN AND SUPPORTED BY THE COILS OF SAID FILAMENT AND A SHIELD OF A HIGHLY REFRACTORY METAL INTERPOSED BETWEEN SAID FILAMENT AND SAID CORE, SAID SHIELD HAVING AN OPENING THEREIN TO PERMIT ACCESS OF GAS TO SAID CORE. 